The present invention relates generally to the field of rotary actuators and more particularly, to a vane type rotary actuator with an improved means for sealing the pneumatic actuation chambers.
In general, a rotary actuator causes the rotation of an output drive shaft through a fixed arc at relatively high, instantaneous torque and relatively low speed. A vane type rotary actuator includes a housing defining an inner chamber, a drive shaft extending through the inner chamber and at least one stationary (stator) vane and one rotating (rotor) vane defining a plurality of actuation chambers. A single vane rotary actuator comprises a single stator vane connected with the interior of the cylinder wall and a single rotor vane connected with the rotating output shaft. By selectively introducing pressurized pneumatic fluid into and exhausting such fluid from the chambers defined between these vanes, the output shaft is caused to rotate, thus permitting it to drive any device where such rotational movement is desired. A single vane rotary actuator, by its very nature, is limited to a rotational arc of less than 360.degree..
A double vane rotary actuator, includes a pair of stator vanes a pair of rotor vanes and a pneumatic accuation chamber between each of these vanes. With a double vane rotary actuator, the torque which can be created with a given pressure is significantly increased. The drawback to a double vane rotary actuator as opposed to a single vane is that it is limited to a rotational arc of less than 180.degree..
One objective in the design and manufacture of all vane type rotary actuators is to provide an effective seal for the accuation chambers so that air or other pneumatic fluid leakage between such chambers can be minimized. One area which has caused particular problems in the manufacture of vane type rotary actuators is the area between the junction of the output shaft, the rotor and stator vane seals and the end cap. In presently existing rotary actuators, this seal is accomplished by an annular end cap seal member which is positioned in an annular groove in the end cap to seal against a portion of the output shaft as well as portions of the stator and rotor vane seals. These end cap seals which have included "O" ring, quad and various other types of seals have rounded corners; thus, there is always a small annular opening between actuation chambers through which leakage can occur. This accordingly reduces the efficiency of the actuator. The prior designs also embody a structure in which a portion of the rotor vane seal engages the end cap seal. This involves contact between one seal member and another, which is normally a rubber to rubber or elastomer to elastomer contact. Because of this contact, the "break away" force, or the force needed to start the vane moving, is quite high and the seal life is quite short.
Accordingly, there is a need in the art for a vane type rotary actuator with improved seal means so as to reduce the "break away" force, increase the seal life and also prevent leakage between the actuation chambers.